If you go to Versiontracker you should find a number of shareware applications out there that will allow you to take the songs off of the iPod and onto your computer without using iTunes. Then, you can move all the songs into iTunes. I'm not sure if the format of the drive would be an issue though, since it was formatted for the Windows machine. If all else fails, you could pull the songs off the iPod onto a windows machine and then transfer them to the Mac.

Kind of a bummer, but shouldn't take more than an hour or two.